1. Field of the Invention
This invention relates to a valve timing control apparatus for internal combustion engines, adapted to control the timing of operations of an intake valve and an exhaust valve of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, the timing of operations of intake and exhaust valves required varies in accordance with the condition of the engine. In most of related art internal combustion engines, a cam shaft is driven by a timing belt via a crankshaft, and the intake and exhaust valve opening and closing time is fixedly determined with respect to an angle of rotation of the crankshaft. However, in recent years, a variable valve timing system has come to be employed for improving an output of an internal combustion engine and reducing an exhaust gas and fuel consumption, and various kinds of valve timing control techniques have come to be disclosed.
For example, the techniques disclosed in Japanese Patent Laid-Open No. 256878/1997 are also included in these valve timing control techniques. The techniques disclosed in this publication are the techniques for driving a cam by changing a phase of rotation of an output shaft of an internal combustion engine, and thereby regulating the timing of an operation of at least one of intake and exhaust valves. These techniques include the steps of detecting the valve timing on the basis of a difference between a phase of the output shaft of the engine and that of a cam, setting a control gain of a valve timing regulator so that a phase of actual valve timing and target valve timing set on the basis of the operating condition of the engine agree with each other, determining a displacement speed of a phase of rotation of the cam on the basis of the transition of the actual valve timing, comparing the displacement speed of this phase of rotation with a normative displacement speed, and correcting the control gain so that a difference between the two speeds is corrected. Thus, a scatter of the displacement speed is offset, and the responsibility and convergence characteristics are improved.
To be exact, this valve timing regulating operation is carried out by outputting when a difference occurs between an actual valve timing and a target valve timing a duty ratio, which corresponds to the compensation for a response delay, and which is determined on the basis of a proportional value and a differential value computed on the basis of the deviation, to a hydraulic control valve, then outputting a duty ratio, which is determined in the same manner on the basis of a proportional value and a differential value computed on the basis of a deviation occurring at a certain point in time, to the hydraulic control valve, retaining the duty ratio until a difference between a target valve timing and actual valve timing becomes not higher than a predetermined level, determining a displacement speed of a rotational phase on the basis of variation of actual valve timing between two points during this duty ratio retaining time and a period of time needed for the occurrence of this variation, comparing this displacement speed with a speed of a normative level, setting small the response delay compensation duty ratio when the displacement speed is higher than the normative level, and setting large the response delay compensation duty ratio when the displacement speed is lower than the normative level.
In a related art valve timing control apparatus for internal combustion engines, a duty ratio determined at a certain point in time is outputted to a hydraulic control valve and retained therein so as to detect a displacement speed in a rotational phase. Therefore, the responsibility with respect to a control operation based on a duty ratio determined on the basis of a proportional value and a differential value computed on the basis of a difference between a target valve timing of each regular predetermined valve timing and an actual valve timing is deteriorated in some cases. In this control apparatus, a displacement speed of a detected rotational phase and a normative speed are compared with each other, and a duty ration is corrected in accordance with a difference therebetween. Therefore, a correction operation is carried out with respect to only a first response delay ascribed to the occurrence of a difference between a target valve timing and actual valve timing. Consequently, it cannot be said that a sufficient correction operation is carried out, so that a sufficient responsibility is not obtained in some cases.
The present invention has been made in view of the above-mentioned circumstances, and provides a valve timing control apparatus for internal combustion engines, capable of obtaining a stable responsibility with respect to a scatter of the construction of a hydraulic control valve occurring during the manufacturing thereof and variation of the valve occurring with the lapse of time, and correcting a scatter of flow rate characteristics by a control operation.
The valve timing control apparatus for internal combustion engines according to the invention is formed so that the apparatus is provided with a cam adapted to be driven by a crankshaft of an internal combustion engine and open and close an intake valve, a cam adapted to be driven by the crankshaft of the engine and open and close an exhaust valve, a valve timing varying means adapted to vary a rotational phase of at least one of the two cams with respect to the crankshaft, a detector adapted to detect an acting position of the valve timing varying means, and a control means adapted to output a control variable for the valve timing varying means, the control means being further adapted to store the characteristics constituting a norm for the valve timing varying means, compute a target valve timing position corresponding to the operating condition of the engine, and determine the control variable of the valve timing varying means with respect to the target valve timing position on the basis of the results of a comparison between a valve timing position detected by the acting position detector and a valve timing position included in the norm-constituting characteristics.
Therefore, a valve timing control apparatus for internal combustion engines, capable of stabilizing the characteristics thereof without being influenced by a scatter of the construction of the valve timing varying means occurring during the manufacturing thereof, offsetting variation of the performance of the apparatus due to the variation thereof occurring with the lapse of time, and alleviating the manufacturing tolerance thereof can be obtained.
The characteristics constituting a norm for the valve timing varying means are formed of model characteristics of a valve timing varying means fixed to an internal combustion engine,so that the valve timing characteristics required by the engine can be maintained as a scatter of the construction of the apparatus is offset.
The acting position of the valve timing varying means is detected on the basis of an angle of rotation of the crankshaft or that of a cam, and this enables the effect identical with that of the first invention to be obtained by the existing detectors, such as a crank angle sensor, etc.